The hypervalent cyclic CF3-iodine reagents[1]

known as Togni reagents (herein referred to as acid CF3 reagent and alcohol CF3 reagent) turned out to be extremely versatile donors of the formally electrophilic CF3-synthon. The success story of the Togni reagents also inspired other research groups to develop other fluoroalkylated analogues of them and explore their potential in electrophilic fluoroalkylation.
In 2008, Hu et al. reported a synthesis of a related (phenylsulfonyl)difluoromethyl hypervalent iodine reagent, utilizing the Umpolung concept known from the Togni reagents. The (phenylsulfonyl)difluoromethyl trimethylsilane, which has shown competence in several examples of nucleophilic difluorosulfonylation and indirect difluoromethylation,[2] was subjected to Umpolung with acetoxy-iodane to give (phenylsulfonyl)difluoromethyl hypervalent iodine reagent in good yield.[3]
In their original report, the stable alcohol PhSO2CF2-reagent could be employed in electrophilic (phenylsulfonyl)difluoromethylation of a variety of thiol substrates in up to 87% yield.
In 2012, Hu et al. demonstrated that the (phenylsulfonyl) difluoromethylation hypervalent iodine reagent can be used for electrophilic (phenylsulfonyl)difluoromethylation of α,β-unsaturated carboxylic acids in the presence of catalytic amounts of an in-situ formed copper complex. Under the applied reaction conditions, acrylate substrates underwent decarboxylation followed by phenylsulfonyldifluoromethylation.[4]
In a publication that followed very soon, the same research group could show that (β,γ-unsaturated carboxylic acids undergo decarboxylation/phenysulfonyl-difluoromethylation to give allylic phenylsulfonyl-difluoromethylated products in good yields. The resulting products could be further transformed into useful difluoromethylated and difluoromethylenated products.[5]
Apart from the (phenylsulfonyl)difluoromethylation hypervalent iodine reagent, perfluoroethyl analogue of acid CF3 reagent was synthesized by Studer et al. who showcased that the resulting reagent can be used similarly as acid CF3 reagent in tandem radical fluoroalkylation/aminoxylation.[6]
Perfluoroethylation is also mentioned in further documents. Mizuta et al. disclose trifluoromethylation of allylsilanes under photoredox catalysis with an indication that also some perfluoroethylation at the allylic position was successful.[13] Zhang et al. discuss mechanistic aspects of perfluoroalkylation. In particular trifluoromethylation.[14] Carboni et al. also deal with perfluoroalkylation, in particular trifluoromethylation, of enecarbamates with one example concerning perfluoroethylaton. [15]
While the (phenylsulfonyl)difluoromethyl substituted reagent has been shown suitable for producing some trifluoromethylated and difluoromethylenated olefins, there is still a need for further fluoroalkylated products.